Faculté des sciences

Bimetallic Metal-Organic Chains, Networks and Frameworks (MOC's, MON's & MOF's) Based on Cyanides: Structure and Physical Properties

Sereda, Olha ; Stoeckli-Evans, Helen-Margaret (Dir.) ; Centeno, T. (Codir.) ; Stoeckli, F. (Codir.) ; Bürgi, T. (Codir.) ; Decurtins, S. (Codir.)

Thèse de doctorat : Université de Neuchâtel, 2008 ; 2013.

Dynamic structural transformations, based on flexible porous frameworks are one of the major challenges for chemists from a fundamental and a practical point of view. The present work deals in particular with the construction of the metal-organic frameworks based on metallocyanies. The metal-organic cyano-bridged frameworks (MOCBF's) synthesized and developed m this thesis have been used for... Plus

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    Summary
    Dynamic structural transformations, based on flexible porous frameworks are one of the major challenges for chemists from a fundamental and a practical point of view. The present work deals in particular with the construction of the metal-organic frameworks based on metallocyanies. The metal-organic cyano-bridged frameworks (MOCBF's) synthesized and developed m this thesis have been used for immersion calorimetry and gravimetrical adsorption studies.
    Tlus thesis is divided into five Chapters. Chapter 1 gives an introduction to the subject of porous coordination polymers and cyano-bridged bimetallic assemblies and on the experimental methods used in this work. Chapter 2 is dedicated to the structural transformations and ferromagnetism (Section 2.2). The "sponge-like' behaviour of the molecular transformations, described in Sections 2.1 and 2.3. are accompanied by a colour change and it has been shown by in-situ X-ray powder diffraction and immersion calorimetry to be completely reversible. In Section 2.2 the two systems studied exhibit ferromagnetism. The first system shows three-dimensional ferromagnetic ordering at ca. 4K. and second shows a weak infra-chain ferromagnetic exchange, as a result of Jahn- Teller elongation in copper (II) ions.
    Chapter 3 describes the studies in the field of immersion calorimetry and adsorption. In Section 3.1 new MOCBF’s are described, two of which show dynamic behaviour triggered by guest removal and inclusion. The dehydration processes, which involve changes in the structures, are reversible, and this was shown using powder X-ray diffraction (PXRD) methods. By a combination of the DSC. PXRD and immersion calorimetry it was possible to find the net heat of the transformation. A remarkable structural transformation, driven by solvent molecules, is presented in Section 3.2. It was found that the two types of reported networks show different behaviour upon drying, falling within the category of "recoverable collapsing" and "guest-induced reformation" frameworks. The methanol adsorption isotherm for the fully out-gassed compound indicates that it is a two step process. Immersion calorimetric studies with different solvents were carried out. By the gravimetric adsorptions studies it was shown that the synthetic strategy based on cyanide-bridged bimetallic assemblies is advantageous for the formation of flexible nanoporous materials.
    Chapter 4 illustrates the different methods used for the construction of MOCBF s and describes their structural properties.
    Chapter 5 describes the adsorption of morphine from aqueous solutions by various nanoporous carbons. It was shown than 99°'o of morphine can be adsorbed in 5 minutes from an aqueous solution by activated carbon PC94-11. with particles of less than 400 μm and an amount in excess by a factor three with respect to the actual saturation capacity. It was found that the main parameters for a speedy elimination are: an excess of carbon, small particles and good initial mixing of the solid with the solution. This specific study has also provided subsidiary information on the affinity coefficient for the adsorption of morphine from aqueous solutions, βs (morphine) = 1-37 ± 0.02. Tins new parameter, of relevance to pharmacology, will allow the prediction of the adsorption equilibrium of this molecule by activated carbons, by using the modified Dubimn- Radushkevich-Kaganer equation.
    In conclusion, this work describes the synthesis and physical properties of new MOCBF" s which exhibit striking structural transformations. Powder X-Ray diffraction combined with adsorption and immersion studies provides insights into these transformations.